Recent advances in technology and techniques have made the use of lasers in surgical procedures increasingly common. The precision attained through the use of lasers and laser equipment has particular advantages in microsurgical procedures which were formerly not possible using conventional instruments. As the field has developed, however, some of the techniques which are now in use and which are theoretically sound have led to previously unforeseen problems.
As an example, the conventional surgical procedure to produce a new outflow path for the aqueous humor in glaucoma patients has consisted of several steps, making the operation complicated and relatively traumatic. As a result, the procedure often fails due to wound healing, which closes the newly formed opening by scarring. Several authors have thus investigated the use of lasers to simplify this procedure and to reduce trauma:
Q-switched YAG laser pulses have been delivered by means of a specially designed mirror-contact lens across the anterior chamber and aimed at the sclera anteriorly to the trabeculum meshwork. The difficulties and uncertainties of this method are: (1) The high energies (50 mj and more) per pulse cause hemorrhages of the iris due to the shock waves. Consequently, the iris base is preoperatively photocoagulated. (2) Special precautions are necessary to not inadvertently penetrate the conjunctiva. The energy per pulse can be reduced by injecting silver oxide intralimbally, which complicates the procedure.
CW-YAG laser was delivered through a sapphire contact probe, which was inserted through the cornea opposite to the area of trabecular meshwork to be perforated, the tissue touched by the sapphire tip was vaporized. There are essentially two difficulties anticipated:
(1) Inserting the sapphire tip is a invasive procedure and;
(2) using a cw: YAG laser causes more thermal damage to remaining tissue than by using short pulsed lasers, thus increasing wound healing reactions and lowering the success rate.
CW ultraviolet laser had been delivered through an optical fiber in a similar way as the sapphire tip described above. The anticipated problems are the same.
308 nm wavelength pulses from an excimer laser had been delivered through an optical fiber the same way as above. Beside the same disadvantage of being an invasive procedure, this wavelength causes high risks because of its phototoxic effects to retina and lens, and because of potential carcinogenic effects.
A 193 nm excimer had been used ab externo after removal of the conjunctiva. This wavelength cannot be transmitted through an optical fiber.